Yes, I have it from several sources that the lightest timber A-cats of the late 80's were 45-50 kg's but they would break their bows of during a pitchpole.
Some moth hulls build out of ply are 15 kg or less (3.55 mtr)
Wouter
Wouter Hijink Formula 16 NED 243 (one-off; homebuild) The Netherlands